Structural, magnetic and dielectric properties of Terbium substituted nanosized Nickel-Ferrites from a new perspective

The current research focuses on the synthesis of nickel spinel ferrite nanoparticles doped with rare earth elements via green synthesis-assisted sol-gel auto combustion method. X-ray diffraction (XRD), field electron scanning electron microscopy (FESEM), Fourier transform infrared spectroscopy (FT-IR), Raman spectra were carried to examine the development of phase, morphology, and crystal structure. Structural parameters, cation distribution, and lattice strain were determined through Rietveld analysis and Williamson-Hall (W-H) plots. The lattice constant shows an increasing trend with increase in Tb³⁺ ion concentration. Using the G-Fourier technique, the electron density mapping of Nickel nano-ferrites replaced with rare earth (Tb) elements was computed. Saturation magnetization and magnetic hysteresis loss was found to decrease with Tb³⁺ addition. The insignificant hysteresis curve with small coercivity value and retentivity seen demonstrates the soft behavior. The room temperature resistivity values increase with the addition of terbium. The observed dielectric dispersion with frequency is explained by the Maxwell–Wagner two-layer model and the electron hopping mechanism, which are responsible for conduction and polarization. The dielectric constant and dielectric loss decrease with the addition of Tb³⁺, which can be attributed to a reduction in the hopping rate due to the substitution of Fe³⁺ ions by Tb³⁺ ions at the octahedral sites. The dielectric behavior of the NiTb_0.1Fe_1.9O₄ composition exhibits a maximum dielectric constant value with a minimal loss tangent. The Cole-Cole plot highlights the role of grains and grain boundaries in the bulk material. Through impedance studies, the resistance and capacitance of both the grains and grain boundaries have been determined. The increased resistivity and reduced dielectric loss attained in Tb doped ferrite is promising as it is desirable for high frequency applications.